Electronic switch



P. C] MICHEL v ELECTRONIC SWITCH July 13, 1943.

Filed Nov. 15, 1941 2 Sheets-Sheet l Joy- Inventor 2 Philip c. Michel,

His A tornea July 13, 1943. MlcHEL 2,324,314

ELECTRONIC SWITCH Fi led Nov. 13, 1941 Fig. 5.

2 Sheets-Sheet 2 inventor" I phh'p C. Michel,

k f"? s Aiiil ma" E; {I

Patented July 13, 1943 2,324,314 ELECTRONIC SWITCH Philip 0. Michel, Schenectady, N. Y.,

assignor to General Electric Company, a corporation of New York Application November 13, 1941, Serial No. 419,035

11 Claims. (01. 250-27) This application is a continuation in part of my copending application for a Counter circuit,

Serial No. 419,034, filed November 13, 1941, as-

signed to the same assignee as the present application.

My invention relates to current controllers and concerns particularly electric discharge circuits which may .be controlled in response to impulses.

It is an object of my invention to provide an improved electronic switch or an improved ionic switch avoiding switching transients in the output circuit.

Other and'i'urther objects will become apparent as the description proceeds.

In carrying out my invention in its preferred form I provide what may be called a scale of two counter circuit and an amplifier circuit. The amplifier circuit is controllable and serves as a switch to control the transmission of signal impulses between input and output terminals. The counter circuit serves as a relay responsive to control impulses for turning the amplifier on and off. The scale of two counter circuit is arranged to be shifted back and forth between two equilibrium conditions by successive control impulses actuating'the counter circuit. The amplifier is arranged to be turned on and oflf by a bias control which is high or low according to the equilibrium condition of the scale of two counter circuit. The circuit which is to be controlled is connected to the input side of the amplifier and the output side of the amplifier either reproduces the current variations of the circuit to be controlled gr not according .to whether the amplifier is turned on or oil. l

A better understanding of the invention will be afforded by the following detailed description considered in connection with the accompanying drawings in which Fig. 1 is a circuit diagram of one embodiment of my invention; Fig. 2 is a set of graphsillustrating the principle of opercharge devices [3 and II are coupled to the first pair of discharge devices so as to be controlled thereby and to have the discharge current shifted back and forth between the discharge devices l3 and It in response to successive input control impulses as described more in detail in my original application.

The counter circuit iihas a pair of input terminals 15 and It, to which the control impulses are adapted to be applied, and has a pair of out-v put terminals l1 and I8 connected to the control circuit of the amplifier 9 in a manner to be described more in detail hereinafter. If desired, the-terminals l6 and 18 may be grounded, together with appropriate points in the circuits of the dis- .charge devices- In the arrangement illustrated the discharge devices are vacuum tubes, the tubes II and I! being shownas of the pentagrid type and the tubes l3 and ll of the triode type. The latter may be combined to form a double triode if desired. The tubes II and [2 have primary control electrodes or #1 grids coupledto the input terminals l5 and I6 through a coupling condenser l9 and are negatively biased by a suitable source 20. As will be well understood by those skilled in' the art the tubes l I and l 2, bein of the pentagrid type, also contain suppressor grids or #5 grids which may be connected to cathodes. The #3 grids serve as auxiliary control electrodes. The #2 and #4 grids may be employed as shield grids for the #3 grids and may be connected to a point at an intermediate potential in the anode voltage source Ill. The grids are, for convenience, designatedby the numbers l to 5, the #1 grid being nearest the cathode.

In the arrangement illustrated the cathodes of the tubes are grounded and the anodes are connected to the positive terminal of the energizing source Ill through anode resistors 25 and 26. The anodes of the tubes l2 and I3 are connected to the source l0 through the resistor 25, and the ation of. the type of scale of two counter circuit illustrated in the drawings, and Fig. 3 is a circuit diagram of a modification of the arrangement of Fig. 1, arranged to be responsive to only the first and second received impulses.

- In the arrangement illustrated in Fig. 1 there is a scale of two counter circuit 8 arranged to control the bias ofv an amplifier circuit The anodes of the tubes H and II through the anode resistor 26. The control electrodes and anodes of the tubes l3 and H are cross coupled by means of resistors 21 and 28 and the control electrodes are negatively biased by connection to a source 29 through resistors 30 and ii. The #3 grids or auxiliary control electrodes of the tubes I I and I2 are coupled to voltage varying pointsin the circounter circuit 8 is energized by a source of anode voltage II, which may be grounded on the negative side, and includes pairs of electric discharge devices I l and [Land [3 and H. Thedevices l land llare responsive to input control impulses and the discuits of the tubes l3 and M, for example, the control electrode thereof, by means of resistance condenser circuits. The coupling circuits may take the form of resistors 32 and 33 connecting the respective auxiliary control electrodes of the tubes I l and I! to the control electrodes of the tubes l3 and i4, and condensers 34 and 35 serving to ground the auxiliary control electrodes of the tubes H and I2 with respect to high frequency or steep transients.

The circuit constants are so chosen that at any given instant either the tube l3 or the tube I4 is conducting and whichever tube is conducting biases the other tube past cutoff. Likewise circuit conditions are such that the potentials to which the supplementary control electrodes of the tubes II and I2 are brought by the current conditions in the tubes I3 and I4 are such that one of the tubes H and I2 is responsive to impulses applied at the primary control electrode #1 grid and the other tube is non-responsive. The transmission'of an impulse through the responsive tube to the tubes l3 and I4 however shifts the current from one of the latter tubes to the other and changes the relative potentials of the supplementary electrodes of the tubes II and I2 so that the other tube of that pair is responsive to the next impulse applied at the primary control electrodes or #1 grids. The output terminal I1 may be connected to a suitable point in the circuit of one of the tubes l3 and I4, for example, to a tap on the resistor 21.

With a wave shape of the input impulses as illustrated in the curve A1 of Fig. 2, the potentials of the primary control electrodes of the tubes II and I! will vary as represented by the curve A: of Fig. 2. Current impulses will accordingly be produced in the tubes II and 12 as represented by the curves I1 and I: respectively of Fig. 2. The control electrode potentials of the tubes l3 and [4 will fluctuate in accordance with square wave shapes as represented by curves D1 and D: respectively of Fig. 2. However, owing to the time delay produced by the condenser resistance coupling between the control electrodes of the tubes l3 and I4 and the supplementary control electrodes of the tubes II and I2, the

- potentials of the latter will follow the logarithmic curves F1 and F: respectively of Fig. 2.

Current is shifted back and forth between the two-equilibrium-mode tubes l3 and I4 by successive impulses actuating the commutating tubes I l and II. The voltage between the output terminals l1 and I! will follow a square wave formed as represented by the curve H of Fig. 2, having half the frequency of the input control wave A1.

The amplifier circuit 3 comprises a pair of electric discharge devices 43 and 44 connected in push-pull relation, each having an anode, a cathode and a control electrode, a pair of rectitying devices 45 and 48 and a suitable constantvoltage device such as a floating voltage source degenerative cathode resistor 43 is connected in the common cathode lead of the tubes 43 and 44 and the regulated voltage impedance 41 is shunted across the anode-cathode circuits of the tubes 43 and 44 through the rectifying devices 45 and 45, respectively, for the purpose of limiting the fall in potential of the cathodes of the tubes and 44 when biased to non-conducting position. If desired one or more stages of push-pull amplification may be provided consisting of pairs of discharge devices such as the discharge devices 49 and 50.

The pairs of discharge devices 43 and 44 and 43 and may take the form of single or double triode vacuum tubes and the rectifying devices 45 and 45 may take the form of diode vacuum tubes or a double diode tube if desired. The

,or a regulated voltage impedance unit 41. A

tubes may be energized from the common anode voltage source ID with the anodes of the triodes connected to the positive terminal of the source l0 through anode resistors 52, 53, 54 and 55, the cathodes of the triodes 43 and 44 connected to the negative or grounded terminal of the anode voltage source I 0 through the degenerative cathode resistor 48, and the cathodes of the triode 49 and 50 connected to ground through a commondegenerative resistor consisting of two parts 56 and 51 in series.

The amplifier 9 has input terminals 58, 59 which may be coupled in any suitable manner to the control electrodes or grids of the tubes 43 and 44 in such a way as to apply potentials of opposite polarities to the latter. The coupling may take the form of a transformer 50, for example, having a secondary winding 5 I, and having a center tap 62 connected to the positive output terminal I1 of the counter circuit 8 for biasing the tubes 43 and 44 in accordance with the condition of the counter circuit 8.

The voltage regulated impedance 41 may take the form of a voltage regulator tube 54, such as a neon tube, for example, of a type in which the interelectrode space breaks down when the voltage exceeds a predetermined value, in series with a resistor 65 with a condenser 65 shunting the series unit consisting of the tube 54' and the resistor 65.

The amplifier tubes 43 and 50 may be resistance capacity coupled to the anodes of the tubes 43 and 44 by means of suitable coupling condensers 61 and 58 and grid-leak resistors 59 and 10, respectively. The resistors 53 and 10 areshown as connected between the control electrodes of the tubes 43 and 50, respectively, and the junction terminal of the degenerative cathode resistors 58 and 51.

As already explained, the application of successive control impulses at the terminals l5 and.

It or the counter circuits causes the voltage at the bias voltage terminals l1 and II to rise or fall according to the square wave H of Fig. 2. The circuit constants are so chosen that the maximum output voltage of the circuit lis above the "o threshold of the amplifier Land the minimum voltage is below the 0115" threshold of the amplifier 3.

My invention is not limited to the use of particular circuit values. However, when triodes of the GFBG type are employed for the tubes 43, 44, 49 and 50 and the maximum and minimum voltages of the wave H are 150 and volts,-respectively, satisfactoryresults may be obtained by utilizing the following circuit constants:

Resistance of resistor 44 ohms- 20,000 Resistance of resistor 55. ..do 1,000 Resistance of resistors 52 and 53 do 500 Resistance of resistor 51'. do 20,000 Resistance of resistors 89 and 1Lmegohm. Resistance of resistor 53 ohms 250 Resistance of resistors 54' and 55 do 2,000 Capacity of condenser 38 microfarad 1 Capacity of condensers 61 and do- 0 Anode voltage from source ll ..volts 300 Type of diodes 45 and 40 6H6 Type of voltage regulator tube 04 VR If desired the regulated voltage source 41 may take the form of a battery of dry cells insulated irom ground, in one the "on" period of the amplifier is expected to exceed the period over 12111111226118 voltage regulator tube 34 will remain When an input impulse is applied which raises the control bias oi the amplifier 9 above the critical value turning the amplifier on, any impulses applied betweenthe input terminals 58 and 59 are transferred to the output terminals H and I2. Owing to the push-pull connection or the triodes the input signal at the terminals 58 and 59 may be amplified appreciably, whereas any transients are only imperceptibly amplified and any line to ground noise is attenuated for the reason that the input signal impulses are in series on the control electrodes of the pairs of triodes being unaflected by the cathode resistors while the transient eflects and line to ground noise or strays are applied to the control electrodes in parallel, causing degeneration or attenuating 'action of the cathode resistors. When the next control impulse is applied at the terminals and I6 lowering the control bias voltage below the critical value and turning ofi the amplifier, input signals at the terminals 58 and 59 are no longer transferred to the output terminals H and 72. There is no perceptible transient produced in the output circuit for the reason that even when the amplifier is in the ofi condition the anode resistors 52 and 53 are carrying current and there is relatively little change in potential of the anodes oi the tubes 43 and 44 whether the amplifier is turned on or off. The potential of the regulated voltage impedance E1 is so chosen in relation to the ignition voltage of the diodes 45 and 46 that when the control electrodes of the tubes 43 and H are biased off," the potential of the cathodes of the tubes 43 and M will remain just above a value preventing conduction or amplification by the tubes 43 and 44. When the tubes 43 and 44 are biased on" by the control voltage from the conductor 63 the potential of the cathodes of the tubes 43 and 44 is lower in relation to the average control electrode potential. Thus, when the amplifier is on current flows through the anode resistors 52 and 53 through the tubes 43 and 44 but when the amplifier is of! current fiows through the anode resistors 52 and 53 through the diodes 45 and 46. Consequently, there is relatively little change in the direct current component of current flowing through the resistors 52 and 53, whether the. amplifier is on or ofi. Therefore, relatively little switching transient is produced and as already explained the push-pull connection of the amplifier tubes 49 and 50 serves to attenuate any switching transient which may remain while amplifying the desired signal.

In the apparatus thus far described the amplifier 9 is turned on and of! in response to alternate received control impulses. However, my invention is not limited to the specific arrangement described. As indicated in my aforesaid parentapplication separate sources of control impulses may be connected to the #1 grids of the tubes H and i2 so that the impulses from one control source can be eflectiveonly to turn the amplifier on and the impulses from the other control source can be 'eflective only to turn the amplifier ofl." In this case, if impulses are received alternately irom the two control impulse sources the amplifier will also be turned on and of! indefinitely. However, the apparatus may also be so arranged as to produce a single on and ofi operation, or vice versa.

If response to only first and second received control impulsesis desired a combination of the scale-oi-two input. commutator section (tubes II and I2) with two separate two-equilibriummode sections may be employed to provide lock-cu action of the scale-oi-two so that the amplifier is turned on and of! (or of: and on) but once until reset of the two equilibrium mode sections. Their reset is efiected by lowering the plate or grid potential of the appropri ate two-'equilibrium-mode triode, either by momentariiy grounding it through a resistor as al ready explained, or by permanently connecting it to the plate or anode of an auxiliary reset" triode having a grid potential which is normally below cutofl and is momentarily raised for'resetting. 7

In Fig. 3 is illustrated a modification of the arrangement of Fig. 1 which may be employed when only one on and of! operation of the equilibrium-mode tubes l3 and H. In the ar- .rangement of Fig. 3 a second pair of two-equilibrium-mode tubes i3 and M is employed. The equilibrium-mode tubes l3 and I4 and i3 and II are so connectedthat when the commutating tube il has been actuated to shift current from the tube E3 to the tube II no further action takes place in this part of the circuit. Likewise when the commutating tube i2 has been actuated in response to the second impulse to shift current from the tube I3 to N no further action takes place. However, a suitable reset circuit 13 may be provided for restoring the tubes I3, H, and I3, i4 to their original condition in a manner which will be described hereinafter.

Inasmuch as the apparatus of Fig. 3 includes two pairs of two-equilibrium-mode tubes instead of only one pair, the scale of two output terminals l1 and it of Fig. 1 are replaced by'a corresponding pair of output terminals 11' and is which are indirectly connected to the output circuits of the tubes l3 and Il through a discharge tube circuit 14, the action of which willbe described more in detail hereinafter; In order that the apparatus of Fig. 3 may be operated either in the normal manner so as to,produce only one on and 01T" operation, or the operation may be repeated as in the case of Fig. 1, a suitable change-over switch 15 is provided which may take the form of a single pole double-throw switch having a movable contact 16 and a pair of stationary contacts 11 and 18. For

connected to the tubes l2 and H to produce the same action as in Fig.- 1. However, when the switch 15 is in the normal position with the circuit closed between the contacts 15 and 11, the commutating tube I! has its anode connected to the anode of the tube ll" instead of the tube ll and therefore serves to commutate the tube ll insteadoi the tube I},

The electric discharge device circuit ll in theiorm illustrated consists of a pair of discharge devices-19 and III and a rectifying device 9|. These devices may take the form oi vacuum the #1 grid from the input terminal I5.

tubes, the tubes I8 and 88 being shown as triodes with anodes, cathodes and control electrodes or grids represented by the customary symbolaand the rectifying tubes 8| taking the form of a diode rectifier. The cathode 82 is connected with the cathode of the triode l8 and the anode 83 is connected in series with a resistor 84 to the cathode of the triode 88. The anodes of the tubes I8 and 80 are connected to a source of anode voltage III' which is common to the tubes 45 and 46 of the amplifier 8, and the cathodes of the tubes 18 and 88 are connected to the negative side of the source I by grounding them through cathode resistors 85 and 88, respectively. The control electrode of the tube 88 is connected to the junction terminal of resistors 21a and 21b which are interposed between the anode of the tube I3 and the control lectrode of the tube I4. The control electrode of the tube 18 is connected to the junction terminal of resistors 28a and 28b which are interposed between the anode of the tube I 4' and the control electrode of the tube I3. The output terminal IT for applying control bias to the amplifier 8 is connected to the anode 83 of the diode rectifier 8|.

The reset circuit 13 consists of a pair of electric discharge devices which may take the form of triode vacuum tubes 81 and 88, having anodes, cathodes and control electrodes represented by the customary symbols. The anode of the tube 81 is connected to the anode .of the tube I3 and the anode of the tube 88 is connected to the anode of the tube I3. The cathodes of the tubes 81 and 88 are grounded. The control electrodes of the tubes 81 and 88 are negatively biased to I cutofi by connection to the source 28 through a suitable resistor and are connected in series with a resistor 88 and a normally open switch 80 to a suitable source of positive potential such as a point on the source ID or a separate battery 8| grounded on the negative side.

When the change-over switch I is in the repeat position the vacuum tube circuit 14 acts merely as a coupling and the action is the same as explained in connection with Fig. 1. When the change-over switch I5 is in the normal position with the contacts I8 and TI together, only one on and oiif action of the amplifier 8 is produced. It is assumed that the two-equilibrium-mode tubes I3 and I3 are initially conducting and that the tubes I4 and I8 are in non-conducting condition or are in the condition of carrying minimum current. As explained in connection with Fig. 1 the commutating tube I I then has its auxiliary control electrode or #3 grid at an elevated potential so that it is in a condition to be responsive to impulses applied at the terminal I5. At the same time the eommutating tube I2 is not in condition to respond to such impulses. When the first control impulse is received at the terminals I5 and IS the commutating tube becomes conducting momentarily and eommutates the tube I4 to shift the current fiow from the tube I3 to the tube I4. This lowers the potential of the #3 grid of the commutating tube II and renders it unresponsive to any further impulses applied to The potential-of the #3 grid of the tube I2 is simultaneously raised so that when the next impulse is received the commutating tube I2 will be responsive thereto.

The eiiect of the shift in current from the tube lit to I4 is to raise the potential of the control electrode of the tube 8|) therefore rendering the latter conducting, passing current through the cathode resistor 86' and raising the potential of the anode 83 of the diode rectifier 8| to cause current to pass through it. Consequently, current fiows also through the resistor 85 and the potential of the output terminal I1 is raised to the value represented by the potential drop in the resistor 85 plus the interelectrode drop in the diode 8|. Accordingly, the grid potentials of the amplifier 9 are raised above the threshold value and the amplifier 8 is turned on.

When the next control impulse is applied to the input terminals I5 and I6 of the counter circuit 8' the tube I2 is, as already explained, in condition to be responsive and transfers the impulse to the anode of the tube I4 causing the latter tube to become conducting. Thus current is shifted from the tube I3 to the tube I4, and the potential of the control electrode of the tube I8 is lowered. Accordingly the flow of current in the tube I8 is diminished or cut off lowering the potential of the cathode of the tube 18 and correspondingly lowering the potential of the output terminal II. The circuit constants are such that this lowering of potential lowers the grid bias of the amplifier 8 below the of! threshold and turns the amplifier 8 off. Any further impulses applied to the input terminals I5 and I6 will have no efiect on the counter circuit 8 since current has already been shifted from the tube I3 to the tube I4 and from the tube I3 to the tube I4, and these pairs of tubes are in their equilibrium condition so that the current does not shift back.

If it is desired to reset the counter circuit 8' to its original condition so that it will perform another on and oil operation the reset switch 88 is closed momentarily which thus raises the control electrode potential of the tubes 81 and 88 causing them to act as short circuits across the anode-cathode circuits of the tubes I3 and I3. This action commutates the tubes I3 and I8 and shifts the current back to them from the tubes I4 and I4.

I have herein shown and particularly described certain embodiments of my invention and certain methods of operation embraced therein for the purpose of explaining its application, but it will be obvious to those skilled in the art that many modifications and variations are possible, and I aim therefore to cover all such modifications and variations as fall within the scope of my invention which are defined in the appended claims};

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An electronic switch with negligible switching transients comprising a pair of electric discharge devices each having an anode, a cathode and a control electrode connected in push-pull relationship, a cathode degenerative resistor, a regulated voltage impedance, a pair of rectifying devices, load circuit connections for energizing the anode-cathode circuits of the discharge devices and connections for applying a variable control bias to the control electrodes oi. the discharge devices and for applying input signal voltage to the control electrodes with opposite polarities, the regulated voltage impedance being connected in series with one of the rectifying devices between the anode and cathode of one of the electric discharge devices and being connected in series with the other of said rectifying devices between the anode and cathode of the other of said electric discharge devices, the regulated voltage impedance being seleotedto have such a voltage in combination with the voltage drop of the rectifying devices as to hold the potential of the cathodes of the discharge devices up to ries with the anode through the energizing conv nections, connections for applying a control bias variable between predetermined limits in the control electrode cathode circuit, the regulated voltage impedance and a rectifying device being connected in series between the anode and the cathode of each electric discharge device, the regulated voltage impedance being selected to have,

a potential difierence of such a value as to limit the potential difference between the anodes and cathodes to a predetermined value just below that sufficient to render the electric discharge devices amplifying when the control bias is at the minimum for turning the amplification oil.

3. In combinatioman electronic discharge device having an anode, a cathode and a control electrode, connections for applying a control bias variable between ,predetermined limits in the control electrode circuit for rendering the discharge device amplifying or non-amplifying, load-circuit connections for energizing the anode-cathode circuit, a cathode degenerative resistor connected in series with the cathode and anode through the energizing connections, a rectifying device and a constant voltage device, said rectifying device and said constant voltage device being connected in series between the anode and cathode of the said electric discharge device, the constant voltage device being selected to have a potential difference of such a value as to limit the potential diflerence'between the anode and cathode to a predeterminedvalue just below that sufficient to render the electric discharge amplitying when the control bias is at a minimum for turning the amplification ofi. r

4. Apparatus of the character set forth in claim 3 including a resistor connected in series with the constant voltagedevice and a condenserconnected across the last-mentioned resistor and the constant voltage device.

5. In combination, a current-controlling device having a voltage responsive control circuit and having an anode and a cathode, connections for energizing the anode-cathode circuit, connections for applying a control bias variable between predetermined limits in the control electrode circuit for rendering the current controlling device relatively conducting or non-conducting, and a voltage regulated impedance connected in circuit between the anode and the cathode of said current-controlling device, the regulated voltage impedance being selected to have a potential diflerence of such a value as to limit the difference between the anode and cathode to a predetermined value just below that sufficlent to render the current controlling device relatively conducting when the control bias is at the minimum for rendering the current controlling device relatively non-conducting.

6. An electronic switch comprising a pair of commutating discharge devices each having an anode, a cathode, a primary control electrode, and an auxiliary control electrode, a pair of twoequilibrlum-n'iode discharge devices each comprising an anode, a cathode and a control electrode with anodes and control electrodes cross coupled and couplings between their respective circuits and the auxiliary control electrodes of the first-mentioned pair of tubes respectively, a second pair of two-equilibrium-mode discharge devices each having an anode, a cathode andea control electrode with cross-couplings between the anodes and control electrodes, commutating connections between one of the commutating discharge devices and one of the devices of the first pair of two-equilibrium-mode discharge devices, commutating connections between the other commutating discharge device and a different one of the devices of the two-equilibri'um-mode discharge devices, an amplifier adapted to be turned on and oil in response to biasing potentials above and below predetermined values having a bias voltage terminal and a coupling circuit interposed between the bias terminal of the amplifier and the circuits of the first device of the second pair of discharge devices and the second device of the third pair of discharge devices for successively raising-and lowering the amplifier bias voltage in response to current shifts in the second and third pairs of discharge devices, the first device of eachiof said second and third pairs of discharge devices being initially in conducting condition whereby a control input impulse ap- I plied to the primary control electrodes of the first pair of discharge devices is transmitted through the first of such devices to the second pair of discharge devices to shift the current, and a second impulse applied to the primary control electrodes of the first pair of discharge devices is transmitted through the second of said devices to the third pair of discharge devices for shifting the current therein. v

7. An electronic switch comprising an amplifier having input bias terminals adapted to have bias potentials applied thereto for turning an amplifier on or oil according to the magnitude oi the potential, a scale of two counter circuit with control impulse input-terminals adapted to have control impulses applied thereto and output terminals connected to the bias terminals of the amplifier for controlling the amplifier, said counter circuit comprising a pair of sections each providing alternate current paths with output connections from said sections to the output terminals of the scale of two counter, and current controlling devices successively responsive for transmitting control impulses first to one of said .altemative currentpathsections' and then to the other from said control input terminals for successively shifting the current paths in said sections and thus raising and lowering the potentials at the output terminals for turning the amplifier on and oil.

8. A current controlling device with a pair of terminals and a voltage responsive control element adapted to have the potential thereof with respect to one of said terminals raised or lowered "for rendering the device relatively conducting'or non-conducting, and a voltage limiting unit. con-,

nected between the terminals of the device for limiting the voltage therebetween to a value below that at which the device can become relatively conducting with minimum control potential applied to the control element whereby relatively little change in voltage between the terminals of the device takes place when it is rendered relatively conducting or non-conducting and switching transients are thereby minimized.

9. Apparatus adapted to be rendered eflective or ineffective to transmit electrical effects referred to as signal impulses in response to the successive application of electrical effects referred to as control impulses and unresponsive to the reception of more than two controlling impulses, said apparatus comprising a principal current controlling device for transmitting the said signal impulses having an electroresponsive control for rendering the device relatively conducting or non-conducting, a double-throw impulse transmitting apparatus having two alternative positions responsive to variation in control -po-' tential, a pair of alternative current path devices'each having control means for rendering one or the other of two alternative current paths therein relatively more conducting than the other in response to electrical impulses and includingelectrical impedance in the-alternative current paths for raising or lowering potentials at points therein in response to variations in current flow produced by relative variations in conductivity,-

and coupling means for transmitting oppositely effective control impulses'from said alternative current path devices to the electroresponsive element of the main current controlling device in response to successive current shifts in the first and second alternative current path devices, the variable potential points of said alternative path devices being connected to the said double-throw impulse transmitting apparatus for making it effective successively to transmit control'impulses first to one .alternative current path deviceand then to the other whereby the first received control impulse is transmitted to the first of the alternative current path devices to shift current therein and transmit a control eflect to the electroresponsive element of the main current controlling device for changing its condition, theswitching apparatus with couplings to the dissecond received control impulse is transmitted to the second of said alternative current path devices for shifting current therein and transmitting a reversely effective control impulse to the electroresponsive element of the main current controlling device for restoring it to its original condition.

10. In combination, a single-pole double-throw switching apparatus having a normal setting and an alternative setting, a pair of electric discharge devices each having an anode, acathode and a control electrode with cross-couplings between the anodes and control electrodes to maintain one or the other of the discharge devices in conducting condition while it biases the other to cut-off, couplings-between the switching apparatus and the discharge devices for transferring impulses transmitted through the switching apparatus to one orthe other of the discharge de-- vices according'to the setting of the switching apparatus, voltage responsive control for the charge devices for transferring the switching apparatus from one setting to the other according to which of the discharge devices is in conducting condition, whereby the application of impulses successively through the switching apparatus transfers conduction back and forth between the discharge devices, and resetting mechanism comprisinga current-controlling device adapted to have its conductivity increased, said latter device being connected across that one of said discharge devices which is conducting with normal setting of the apparatus for lowering the anode potential of said last-mentioned discharge device, transferring conduction to it, and restoringthe apparatu to' its'normal setting, if in the alternative setting.

, 11. Apparatus of the character set forth in claim 10 in which the current-controlling device is an electric discharge device having a control electrode adapted to be energized for resetting the apparatus.-

PHILIP C. MICHEL. 

